Method for treating vegetable material with a view to producing paper pulp



Unite States Paolo Marpillero, Milan, Italy, assiguor to Societe Francaise du Xylcn, Nice, France, a corporation of France Application January 10, 1958 Serial No. 708,059

Claims priority, application France January 15, 1957 No Drawing.

2 Claims.

It is a known fact that it is possible to provide for'the removal of the ligneous components and in an auxiliary manner for the bleaching of vegetable material with a view to producing paper pulp, by treating the vegetable material in an acid medium by means of chlorates activated in the presence of catalysts such as vanadium, molybdenum or the like salts.

' Whereas the application of this method to vegetable material such as straw has appeared of advantage, the same treatment when applied to other materials such as wood leads to certain difficulties. As a matter of fact,

' when wood is subjected to such a treatment, it is found that the cellulosic fibres obtained after the removal of the L'gneous components are weakened.

Starting from the same wood, to which the same extent of removal of the ligneous components is applied, the fibres from which the ligneous components have been removed through activated chlorates, are weaker in the final pulp than those which have been treated by sulfates in accordance with conventional methods.

Furthermore, such a treatment of the Wood leads to a high consumption of chlorates and to a long duration of reaction whereby the method loses its economical interest.

My invention has for its object to cut out such drawbacks and to allow an efiicient application of the methods resorting to activated chlorates to wood and the like material with a view to obtaining cellulosic fibres, having an excellent mechanical resistance, without this leading to an excessive consumption of the reagents or to an exaggerated duration of reaction.

My improved method is characterized by the fact that the hemicelluloses are removed from the raw material before the actual treatment through activated chlorates is applied.

The removal of the hemicelluloses may be obtained by subjecting the vegetable material undergoing treatment to any suitable reagent adapted to dissolve such hemicellulosic compounds. I may resort for this purpose for instance to an alkaline substance, such as an aqueous solution of caustic soda in moderate concentrations below The advantage of the removal of the hemicelluloses before their treatment through chlorates is ascribable as far as I am aware to the fact that said compounds lead to hydrolytic reactions in the presence of chlorates in an acid medium; this produces first hexoses or pentoses, which compounds are subsequently oxidized by the chlorates when the hemicelluloses remain in the substances undergoing treatment. This formation of hexoses or pentoses is obviously highly objectionable since it leads to a considerable consumption of chlorates and to a detrimental action on the grade of the fibres obtained. The preliminary removal of the hemicelluloses allows carrying out the chlorate method without such objectionable reactions occurring.

The solution dissolving the hemicelluloses may be used at room temperature or at a raised temperature below boiling point. It is necessary to let the operation last enough time for the solution to enter in a uniform manner throughout the treated material.

The dissolving action of caustic soda or the like suitable solvent is furthered by a preliminary coarse crushing of the raw material in the presence of the solution or again by a series of mechanical alternatingly compressing and releasing operations, the object of which is to further the penetration of the solvent inside the mate rial undergoing treatment. A series of modifications of the hydrostatic pressure may lead to the same result.

The removal of the residual solvent after operation and also 'of the more or less solubilized hem'icelluloses may be furthered by subjecting the material undergoing treatment to repeated pressure applications which may be accompanied by some degree of crushing if desired These operations may be carried out in conventional apparatus.

When caustic soda is used for the removal of hemicele luloses, a slight addition of sulfur S or of sodium sulfide Na s in amounts corresponding to 5 to 20% of the soda used may exert a favorable action. After removal of the hemicelluloses, the raw material, Whether crushed or otherwise, is subjected to the treatment through activated chlorates in an acid medium with a view to removing the ligneous components.

This treatment of the vegetable material produces a partial solubilization of certain components and chiefly of the lignin so that these components are dissolved in the acid medium. A further amount of these components, being soluble in a neutral or alkaline medium, may be removed through subsequent washing of the material.

It has been found however that a larger removal of such components may be obtained when, after treatment with activated chlorates in an acid medium, the vegetable material is subjected to a treatment with sulfites, for instance sodium sulfites Na SO in a neutral or alkaline medium or again by sulfites in an acid medium, for instance with acid sodium sulfite NaHSO The concentration of the sulfites may be lower than 10% and the temperature lower than C. when the duration .of treatment ranges between 4 and 6 hours. f

After a treatment with caustic soda followed by a treatment with activated chlorate and possibly a further treatment with sulfites, the material is defibrated and transformed into a paste or pulp in conventional machines. Said pulp may be used in an unbleached condition or it may be subjected to bleaching treatment carried out in accordance with conventional methods.

This modus operandi is generally sufficient when wood of deciduous or resinoustrees is subjected to treatment and when unbleached or partly bleached pulp is required. However it may otherwise be suitable to repeat once more the sequence of operations disclosed.

The raw material, after it has been treated with activated chlorates is then subjected to a second treatment with caustic soda, possibly in the presence of S or Na S in a manner similar to the first treatment referred to or preferably to a treatment with sulfites and thenafter, if required, to a second treatment which is similar to the first treatment with'activated chlorates followed, if desired, by a further treatment with sulfites.

The treatments with activated chlorates and the treatments with sulfites following the first treatment have for their final result a reduction in the extent of lignifica tion of the material undergoing treatment, said extent being readily defined through conventional means.

This leads to such a softening of the material undergoing treatment that the latter may be subdivided into elementary fibres through conventional means, which allows obtaining pulps the mechanical resistance of which for the same raw material and for an equal degree of re- Patented Mar. 22, ISQQ.

. 3 moval of the'ligneous components may be equal to or higher than the resistance of Kraft pulps.

The following examples which are not to be construed in a limiting sense describe various embodiments of my invention.

' Example 1 100 kg. of shavings of spruce woodconsidered as dry and of the size generally used for the purposes of the cellulose treating industries are subjected to the action of a.solution containing NaOH at a concentration of 5% and Na s at a concentration of 0.5% during five hours at .aTtemperature of 60 to 90 C. This immersion of the shavings in the alkaline solution maybe accompanied by an of theconventiona l means intended to further the penetration. of the soda inside the wood shavings which may lead toa reduction in the duration of reaction mentioned.

' After this treatment, the shavings are compressed repeatedly in the presence of water with a. view to removingthe major partof the solution impregnating them.

This last operation may for instance beexecuted inside, a vsmall milling apparatus during about one quarter of an hour, which has for its result ,a predetermined amount of crushing of the'sha'vings which arethus-transformed into a mass of very coarse fibres.

The fibrous material obtainedwith a yield of about 80% is then subjected to the action of the activated chlorates. I

When the concentration of the activated chlorates used is equal to 1%, the temperature to 60 C. and the duration of operation to 6 hours, the amount of chlorates absorbed is equal to 4 to 6% of the material undergoing treatment considered in its dry condition. The material may then be either:

(a) Washed and defibrated or ground to form a pulp with a yield of about 75% inside a grinding mill of the disc type or any other well known apparatus.

(5) Or treated with a solution containing about 3% of 'Na sQ at 90 C. during 4 hours, after which it is treated as disclosed at (a') hereinabove.

'(c) r again the treatment according to (b') may be followed before the subsequent treatment according to (a) by a treatment with activated chlorate, with a consumption of about 3% of chlorate after which it is subjcted to treatment with hypochlorite containing 5 to 6% of active chlorine so asto produce a bleached pulp. Instead of said bleaching treatment, any other bleaching treatment may be applied.

Example 2 '-100'kg., as measured in a dry condition, of branches of coniferous wood having an average :diameter of 2 to '5 cm. and carrying their entire bark are cut into shavings having the same size as in the case of Example 1. These shavings are dipped in a solution of caustic soda as in the'case of Example 1 and are washed in the same manner. The yield obtained is equal to 70 to 75%. T116 assent r material including wood and bark being treated with activated chlorate as in the case of Example 1, it is'found that, as a result of an action of the chlorate, the bark is bleached rapidly and in fact before the wood.

I obtain thus, when operating in accordance with (a) or (b) of Example 1, an unbleached pulp with a yield of to from which all traces of bark have disappeared. Said pulp may be used as it is or else it may be partly bleached through conventional means .or again, and as in the case of (0) of Example 1, it may be treated so as to produce a pulp of a perfect cleanliness.

Example 3 100 kg. of branches of broad-leaf Wood similar to those of Example 2 are treated in the manner disclosed in Example l. The pulp obtained after the treatment according to (a) which has been partly bleached by 4%v of Na O may be given a bleaching grade equal to at least 55 GE which allows its use in the production of paper for printing purposes. The same paste may reach through a subsequenttreatment with 6% of hypochlorite a degree of whiteness equal to to 8[) GE.

What I claim is:

1. In a method of deliguification of vegetable wood, used for obtaining paper pulp by' a treatment of said Wood by chlorates activated by catalysts at a temperature lower than C., the improvement consisting in treating the said wood by an alkaline solution at a concentration lower than 10%, at a temperature lower than C., and removing the hemicelluloses before the treatment with chlorates while retaining substantially all of the lignin in the wood.

2. The method of producing bleached and cleaned pulp material from comminuted wood which comprises treating the raw, comminutecl wood with alkali having a concentration of less than 10% and at a temperature below 100 C. for a period sufficient to dissolve the hemicelluloses present in the Wood, removing the alkali and hemicelluloses dissolved therein while retaining substantially all the lignin in the wood, treating the wood, freed of hemicellulose resulting from the alkali treatment, with a chlorate activated by catalysts selected from the group consisting of vanadiumand molybdenum salts in an acid medium at a temperature below 80 C., defibrating the wood to form a pulp, and subjecting the so-treated pulp to a hypochlorite bleaching treatment.

White: Mechanism of the Chlorination of Lignin,Tappi sec., pages 299-309 (particularly page 300), Dec. 11, 1941. 

1. IN A METHOD OF DELIGNIFICATION OF VEGETABLE WOOD, USED FOR OBTAINING PAPER PULP BY A TREATMENT OF SAID WOOD BY CHLORATES ACTIVATED BY CATALYSTS AT A TEMPERATURE LOWER THAN 80*C., THE IMPROVEMENT CONSISTING IN TREATING THE SAID WOOD BY AN ALKALINE SOLUTION AT A CONCENTRATION LOWER THAN 10%, AT A TEMPERATURE LOWER THAN 100*C., AND REMOVING THE HEMICELLULOSES BEFORE THE TREATMENT WITH CHLORATES WHILE RETAINING SUBSTANTIALLY ALL OF THE LIGNIN IN THE WOOD. FACE BETWEEN SAID NICKEL PLATING AND SAID METAL SURFACE. 